Brake servo unit

ABSTRACT

A brake power booster with a brake power booster housing has at least one vacuum chamber and at least an additional pressure chamber, into which ambient pressure can be admitted during the actuation of an actuating pedal for the brake system of the motor vehicle. The actuating pedal is connected to the brake power booster. A vacuum can be established in the pressure chamber in the non-operative position of the actuating pedal, wherein the vacuum chamber and the pressure chamber are separated from one another by a displaceable piston. The brake power booster has at least one additional vacuum chamber, which can be connected to the pressure chamber via a switching device. The switching device establishes the connection between the pressure chamber and the additional vacuum chamber during the return of the actuating pedal after the actuation process.

FIELD OF THE INVENTION

The present invention pertains to a brake power booster for motorvehicles with a brake power booster housing, at least one vacuum chamberand at least one additional pressure chamber, into which ambientpressure can be admitted during the actuation of an actuating pedal forthe brake system of the motor vehicle, which actuating pedal isconnected to the brake power booster, and into which the vacuum can beestablished in the non-operative position of the actuating pedal. Thevacuum chamber and the pressure chamber are separated from one anotherby a displaceable piston. Furthermore, the brake power booster has atleast one additional vacuum chamber, which can be connected to thepressure chamber via a switching device.

BACKGROUND OF THE INVENTION

To assist the driver of the motor vehicle in the case of a brakingoperation and to provide additional braking power for actuating thebrake system, brake power boosters of this type are now customarily usedin the automobile industry. To boost the brake power, the assistance ofthe vacuum generated by the engine is utilized, and the brake powerintroduced into the brake system by the pivoting of the actuating pedalcan be boosted up to fivefold. This is achieved, in principle, by thevacuum generated by the engine being admitted into both the vacuumchamber and the pressure chamber of the brake power booster in thenon-operative state of the brake system so that they are at equilibrium.A pivoting of the actuating pedal of the brake system interrupts theconnection present between the two chambers and opens the rear pressurechamber of the brake power booster, which faces the actuating pedal, tothe atmospheric air, so that air under atmospheric pressure can flowinto this pressure chamber. The piston located between the vacuumchamber and pressure chamber is displaced by the atmospheric pressure,together with the diaphragm connected thereto, in the forward direction,i.e., in the direction of the engine and the pivoting movement of theactuating pedal is thus assisted, and the movement of the piston acts onthe piston rod of a connected main brake cylinder via suitabletransmission members. After the end of the pivoting of the actuatingpedal, the interrupted connection between the pressure chamber, thevacuum chamber and the engine-side vacuum connection is againestablished, so that a rearward movement of the actuating pedal into itsstarting position is made possible.

It is problematic for the use of this prior-art brake power booster thatthe necessary vacuum can no longer be provided to the sufficient extentby the modem gasoline and diesel engines being increasingly used. Thisapplies especially to engines with fuel injection, in which the vacuumgenerated by the engine is no longer sufficient to bring about thedesired additional boosting of the brake power and the necessary brakingdynamics. This problem is remedied by the use of additional vacuumpumps, but they are disadvantageous because they require space for theirinstallation and, in addition, also cause a rather substantial increasein the manufacturing costs of the entire brake system.

Increasing the area of the piston of the brake power boosters used isalso ruled out as a possible solution because of the limited spaceconditions in the engine compartments of modern motor vehicles.

SUMMARY AND OBJECTS OF THE INVENTION

The object of the present invention is therefore to further improve abrake power booster for the brake system of a motor vehicle such that asufficient amount of vacuum is always present for a sufficient number ofsuccessive braking operations with a simple design. The costs for such abrake power booster shall increase only slightly, if at all, comparedwith the brake power booster variants used hitherto.

A brake power booster with a brake power booster housing has at leastone vacuum chamber and at least an additional pressure chamber, intowhich ambient pressure can be admitted during the actuation of anactuating pedal for the brake system of the motor vehicle. The actuatingpedal is connected to the brake power booster. A vacuum can beestablished in the pressure chamber in the non-operative position of theactuating pedal, wherein the vacuum chamber and the pressure chamber areseparated from one another by a displaceable piston. The brake powerbooster has at least one additional vacuum chamber, which can beconnected to the pressure chamber via a switching device.

According to this technical teaching, it is advantageous for theswitching device to establish the connection between the pressurechamber and the additional vacuum chamber after the return of theactuating pedal after the actuation process.

The additional vacuum chamber forms an energy reservoir here, which canbe used during the braking operation and is charged from the engineduring time periods during which no braking operation takes place. Thestorage of the vacuum guarantees that the low vacuum still provided willbe sufficient for a sufficient number of braking operations even in thecase of the modern motor vehicle engines currently in use. Theadditional vacuum reservoir ensures that the vacuum necessary during thereturn of the piston of the brake power booster is also sufficient for arapid succession of braking maneuvers despite the weak suction effect ofthe engine. The special design according to the present invention doesnot require an additional foreign energy source but only additionalcosts due to the provision of a suitable switching device, with whichthe additional vacuum chamber can be connected to the pressure chamber.

It proved to be particularly advantageous for the additional vacuumchamber of the brake power booster housing to be arranged in astiffening cavity. Stiffening cavities made in plastic within the brakepower booster housing are common and present in all customary designs ofbrake power boosters because of the necessary strength of the brakepower booster housing. These cavities can be utilized in the manneraccording to the present invention without enlarging the overallinstallation volume of the brake power booster for the necessaryadditional vacuum chamber. Thus, there are no additional costs due to anexternal vacuum reservoir connected to the brake power booster.

According to another embodiment of the present invention, provisions aremade for the switching device to be designed as a solenoid on-off valve.

An exemplary embodiment of the subject of the present invention will beexplained in greater detail below on the basis of the drawing attached.

The various features of novelty which characterize the invention arepointed out with particularity in the claims annexed to and forming apart of this disclosure. For a better understanding of the invention,its operating advantages and specific objects attained by its uses,reference is made to the accompanying drawings and descriptive matter inwhich a preferred embodiment of the invention is illustrated.

BRIEF DESCRIPTION OF THE DRAWINGS

In the drawings:

FIG. 1 is a sectional side view through the brake power booster of amotor vehicle with an actuating pedal arranged at the brake powerbooster.

DESCRIPTION OF THE PREFERRED EMBODIMENT

Referring to the drawings in particular, the brake power booster,designated by 1 in its entirety, has a brake power booster housing 2,which comprises an engine-side housing bell 3 and a rear housing bottom4 facing the actuating pedal 5. Both the housing bell 3 and the housingbottom 4 are made of plastic. The housing bottom 4 has a mounting block6, on which the upper, free end of the actuating pedal 5 is articulatedin a pivot bearing 7. A diaphragm 8 made of an elastic material,preferably rubber, which is axially displaceable together with a piston9 in the direction of the principal axis 10 of the brake power booster1, is arranged inside the brake power booster housing 2. The piston 9and the diaphragm 8 are connected to an actuating rod 11, which ismounted with its free end projecting from the brake power booster 1 inan elongated hole 12 of the actuating pedal 5.

The drawing attached shows the brake power booster according to thepresent invention in both a non-operative position I (shown at the topof the Figure) and a brake actuation position II (shown at the bottom ofthe Figure), in which the actuating pedal 5 (shown by dash-dotted line)has been pivoted forward, in the direction of the engine compartment, bythe driver of the vehicle. The non-operative position I of the brakepower booster is shown in the upper area above the principal axis 10,while the actuation position II is shown below the principal axis 10 inthe lower area of the brake power booster 1. It appears clearly that avacuum chamber 13, to which vacuum is admitted, is present in thenon-operative position I between the front, engine-side wall of thebrake power booster housing and the piston 9. A vacuum is alsoestablished by admission to the opposite side 14 of the piston 9 in thenon-operative position and this side forms a pressure chamber 14,designed as a narrow gap, in the non-operative position. The pressurechamber 14 is limited toward the housing bottom 4 by a wall 16. Aplurality of stiffening ribs 15, which define a closed additional vacuumchamber 17 due to their arrangement, are located between the wall 16 andthe outside of the brake power booster housing. This additional vacuumchamber 17 is connected via a switching device 18 to an engine-sidevacuum connection, which is not shown here specifically for clarity'ssake.

The vacuum generated by the engine is admitted into both the vacuumchamber 13, the pressure chamber 14 and the additional vacuum chamber 17in the non-operative position I.

If the actuating pedal 5 is brought into the position designated by IIin the drawing within the framework of a braking operation, theconnection between the pressure chamber 14 and the engine-side vacuumline is interrupted. At the same time, a connection is established tothe ambient air, so that atmospheric pressure is now admitted into thepressure chamber 14 and the pivoting movement of the actuating pedal isassisted by the admission of pressure to the piston 9 in the directionof the arrow P. The end position of the pivoting movement of theactuating pedal 5 in the partial view II shows that the vacuum chamber13 has been made substantially smaller by the axial displacement of thepiston 9, whereas the volume of the pressure chamber 14 has increasedappreciably compared with the non-operative position I.

To make possible a rearward movement of the piston 9 in conjunction withthe pivoting back of the actuating pedal 5, the switching device 18establishes a connection between the additional vacuum chamber 17 andthe pressure chamber 14 after the end of the braking operation. Theadmission of pressure to the piston 9 is thus eliminated, so that theentire brake system can again return into its non-operative position,assisted by suitable spring forces. A repeated pivoting of the actuatingpedal 5, performed immediately after the return into the non-operativeposition, leads to the repeated admission of atmospheric pressure intothe pressure chamber 14 and thus to a repeated displacement of thepiston 9 in the direction of arrow P. A plurality of successive brakingoperations are possible with corresponding assist by the brake powerbooster due to the vacuum stored within the additional vacuum chamber,without a decline of the brake-assisting power taking place, even if theconnected motor vehicle engine would not be able alone to provide asufficient vacuum during the rapid succession of the braking operations.

A sufficient vacuum is thus always made available for the actuation ofthe brake system of the motor vehicle without increasing the volume of aprior-art brake power booster. Thus, the performance of the vacuum brakepower system is improved without additional drives or foreign energysources being used; in addition, only extremely low additional costsarise due to the use of a suitable switching device, which can beembodied in the form of a solenoid on-off valve.

The brake power booster according to the present invention shown in thedrawing is a so-called one-step variant. In many areas of motor vehiclemanufacture, two-step variants are used to increase the brake power, inwhich two pistons, to which pressure is admitted, move together withinthe brake power booster housing. The design according to the presentinvention is, of course, also possible in this variant by making theadditional vacuum chamber according to the present invention able to beconnected to the respective pressure chambers of the individual pistons.

In addition, it is, of course, conceivable to divide the additionalvacuum chamber, corresponding to the design characteristics of the brakepower boosters used, into a plurality of individual chambers, whichtogether provide the necessary vacuum for a number of brakingoperations.

While specific embodiments of the invention have been shown anddescribed in detail to illustrate the application of the principles ofthe invention, it will be understood that the invention may be embodiedotherwise without departing from such principles.

What is claimed is:
 1. A brake power booster, comprising: a brake powerbooster housing with at least one vacuum chamber and at least anadditional pressure chamber, into which ambient pressure is admittedduring the actuation of an actuating pedal for a brake system of a motorvehicle, the actuating pedal being connected to the brake power booster,a vacuum being established in the non-operative position of theactuating pedal; a displaceable piston separating said vacuum chamberand said pressure chamber from one another; a switching device; and atleast one additional vacuum chamber, which is connected to the pressurechamber via said switching device, said switching device establishing aconnection between said pressure chamber and said additional vacuumchamber during a return of the actuating pedal after actuation.
 2. Abrake power booster in accordance with claim 1, wherein said additionalvacuum chamber is arranged within said brake power booster housing in astiffening cavity.
 3. A brake power booster in accordance with claim 1,wherein said switching device is designed as a solenoid on-off valve.